Headset - Difference betweeen 3.5mm jack or USB?
Keep in mind that, if you set up the USB headset, you will have essentially TWO soundcards in your computer - your onboard audio or PCI soundcard, plus the USB audio device. You may need to configure Windows to route audio to the USB headset, but you won't need to unplug your speakers. The performance of a typical USB headset is FAR worse than a dedicated gaming-oriented soundcard (Such as the Live!, Audigy, or X-Fi) because your CPU will be doing the 3d audio computation instead of the soundcard itself. It's not likely to be worse than onboard audio, though.
On the other hand, an analog headset simply plugs into the line out and mic in ports in your soundcard. No configuration necessary, most speakers with headphone jacks simply mute themselves when headphones are inserted. The downside is that most speakers don't have a mic passthrough, so you will need to connect the mic plug to the back of your computer.
However, if you have functional front audio jacks, problem solved. Keep the speakers plugged in the back, headphones/mic in front, and enjoy.
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plat-y-pus man n.: an adult male human, that attempts to mate frequently, but spends most of its time alone.